Lanes were closed and traffic was backed up for nearly 12 hours Tuesday after a Greyhound bus overturned in South San Jose, killing two of the 20 passengers on board.

The solo crash happened at 6:38 a.m. on northbound Highway 101 in the HOV lane, at the northbound Highway 85 carpool ramp. The bus left Los Angeles at 11:30 Monday night and was due to arrive in Oakland at 8:10 a.m.

It was raining and roads were wet when the Greyhound bus approached the Highway 85 turnoff on northbound 101. A driver saw the bus making the transition when suddenly, the bus struck the impact barrels at the divider and land on its side.

The 17-ton bus landed on its side after striking a formation of barrels used to cushion impact if a vehicle plows into the divider. A driver who was behind the bus told the CHP that the bus was moving at the speed limit and appeared to be making a safe transition from Highway 101 to Highway 85.

Officer Chris Miceli, with the Hollister-Gilroy CHP office, said the Greyhound bus driver recalled "striking the median barrier, and then the next thing he remembered was the bus at rest on its side like it is here, and that's about all he could tell us."

Two female passengers were killed and one of them was identified as 51-year-old Fely Olivera of San Francisco. Investigators said the two women died after being ejected through the front windows of the bus.

One man was seriously injured and nine others, including the driver, suffered minor injuries. They were taken to nearby hospitals and 10 others were transported by a chartered bus to San Francisco. The CHP confirms the Greyhound bus had seat belts.

A camera on board the bus may provide key details as to what happened.

"There is a camera in the bus, and we're not clear as to what kind of video image, if any, was captured of the collision, but that's definitely something that we're going to look at," Miceli said.

According to the CHP, the bus driver -- identified as 58-year-old Gary Bonslater -- admitted he was tired, but did not say he fell asleep at the wheel.

Bonslater met with a representative from the district attorney's office and is cooperating with the investigation. Authorities do not think drugs or alcohol were involved.

ABC7 learned, this particular Greyhound bus has been inspected three times and no mechanical defects were ever found.

The Los Angeles to Oakland bus made a stop in Avenal and Gilroy where two passengers got off.

Family and friends who want to check on their loved ones who were on the bus can call 1-800-972-4583.

Some of the debris from the collision ended up in the southbound lanes, lodging underneath one car, but it did not cause any injuries. Two northbound lanes were closed all day while the CHP's elite investigation team reviewed every skid mark and potential clue. The NTSB is also sending in a team to run a parallel investigation.

Around 5 p.m. a tow truck carried the bus away to the CHP yard, where investigators with the NTSB will examine it. The investigation could last for months. Investigators plan to go through all the mechanical systems of the bus, trying to rule out any probable cause and they will review possible driver error.

Among the passengers transported to local hospitals, three are in stable condition, three are being treated for minor injuries and three have been treated and released. A child was among the injured and was treated for minor injuries.

Company spokeswoman Lanesha Gipson says the bus driver began his shift in Los Angeles and that the company requires operators to rest nine hours between trips. Authorities say the driver will be asked to submit a blood sample to test for alcohol and drugs.

"They'll look into the driver for the past 24 hours, get a 24 hour profile on the driver and see what he's done over the past 24 hours," said CHP Sgt. Lisa Brazil.